Twitter, Facebook and Google can all burn for all I care. Never used Twitter until I got into Crypto and stopped using Facebook long before. I am trying to disentangle myself from google but it is hard. I do not use their search anymore and I use another provider for some emails. Decentralization is a threat to their respective platforms.
I completely agree with you.
I don't trust ads from these services because they don't check for reliability of the advertisers. And their ban is directly connected to US trying to take control of all the cryptos in their country.
At the end of the day it will be against their own benefit. It makes no sense to decide to ban every add, given that, for example, most weight loss methods are scams an nobody seems to ban them
May be they are not banned because
1. there are few complaints
2. the amounts of loss of deceived clients is not comparable with the amounts of loss on scam ICOs.